Color characteristics of dye-containing inks play an important role in the quality of the printed ink-jet image. Perceived color quality can be characterized using any one of several color space systems, such as CIELAB or Munsell, as is well known in the art. With respect to Munsell color space, a given color is defined using three terms, namely Hue, Value, and Chroma. With respect to CIELAB color space, a color is defined using three terms L*, a*, and b*. With this system, L* defines the lightness of a color, and it ranges from 0 to 100 (with 100 being white). Additionally, the terms a* and b*, together, define the hue, where a* ranges from a negative number (green) to a positive number (red), and b* ranges from a negative number (blue) to a positive number (yellow). Additional terms such as h° (hue angle) and C* (chroma) are used to further describe a given color, as is known to those skilled in the art. A single ink-jet ink of a first color that has good chroma, gamut, hue angle, and lightfastness is not always optimal for use with other colors. In other words, not only does an individual color, i.e., cyan, magenta, or yellow, have to have acceptable color qualities, but the ink-set in which it is used also plays a role in whether the ink-jet ink performs in an acceptable manner. Thus, the appropriate combining of certain inks together in an ink-set can improve image quality.
Accordingly, investigations continue into developing ink formulations that have improved properties and that do not improve one property at the significant expense of the others. Additionally, dye and ink combinations to form optimized dye sets and ink sets, respectively, is also a focus of investigation. Many challenges still remain to further improve the image quality, airfastness, chroma, and lightfastness of ink-jet prints without sacrificing pen performance and reliability.